Drilling and Riveting. 353 , All the plates are now prepared, and must next be marked off for drilling. First the tube holes are carefully lined on the two tube plates, and cut out by pin-drills in a radial machine. Then the outer plates may have their seam rivets spaced out, and one in every six drilled, always omitting the corner holes, or those where three plates overlap. The various parts may now be bolted together, and all the rivet holes drilled and countersunk. Thus K and Q being connected, the tube-plate rivet holes may be done in a radial drill; adding plate j, the circular seams may be drilled, as described at page 308, including also the holes in the dome-hole stiffening piece, and those for the smokebox plate. The dome flange is marked from the boiler and drilled separately. Bolting H to j, the firebox shell may be drilled round its circum- ference in like manner, but those on the flat sides would be done under a radial or multiple drill, the latter being preferable. The barrel is now disconnected from the firebox shell, and the firebox bolted to the latter; then the whole shell placed on the lower table of the Multiple Drill in Plate XIV., and the stay holes drilled right through both plates to secure accurate alignment. All remaining holes are now made, such as those for the angles T, w, and P ; for the seatings v and M ; for the palm stays at s^'and for the guide stays at E. The operation of riveting is clearly shewn at Plate XV. The barrel and shell are closed by fixed riveter at A and o, and the firebox partly by o and partly by portable riveter. Then the smokebox plate and the firebox are each fastened to the boiler shell by portable machines, as shewn at G, L, and H. Finally, the dome may be riveted as at P, so there is no occasion for hand work on any part of the boiler. Note that the angles w, T, and P must be riveted before the firebox is put in. The tubes are fixed by expanding at the smokebox, and beading and ferruling at the firebox end, using the tools in Figs. 304 and 305 -, and the smokebox ends of the tubes are then cut off by the tool in Fig. 306. The screwing of the stays will be understood from the marine example, but in this case their ends are riveted over by hand after fixing. The mudholes are tapped to suit the plugs, the guide stays screwed into place, and the steam pipe M expanded into the plate The boiler is lastly caulked throughout and tested.